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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.lang.c++
Subject: Re: Why can't I understand what coroutines are?
Date: Fri, 09 Aug 2019 19:49:57 -0700
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Xref: csiph.com comp.lang.c++:67509

"Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> writes:

>> [...]
>
> Anyway, to avoid [a recursive coroutine] I'd probably do
> something like this:
>
>
> auto bftraverse( Node* root )
>     -> optional<Data>
> {
>     stack<Node*> nodes;
>     nodes.push( root );
>     while( not nodes.empty() ) {
>         const auto p = nodes.top();
>         nodes.pop();
>         if( p == nullptr ) {
>             co_return {};
>         }
>         co_yield p->data;
>         if( p->right ) { nodes.push( p->right ); }
>         if( p>left )   { nodes.push( p->left ); }
>     }
> }

The function body can be simplified thus:

    stack<Node*> nodes;
    nodes.push( root );
    while( not nodes.empty() ) {
        const auto p = nodes.top();
        nodes.pop();
        if( !p )  continue;
        co_yield p->data;
        nodes.push( p->right );
        nodes.push( p->left );
    }